Consider a circle whose size can vary. Let r represent the radius of the circle (in cm) and let C represent the circumference of the circle (in cm). Suppose the function f determines the circumference of the circle in cm, C, given its radius length in cm, r. a. Write a function formula for f. f(r) = Preview b. What does f(18) represent in this context? Select all that apply. OA circle with a circumference of 18 cm. The radius (in cm) of a circle whose circumference is 18 cm. OThe circumference (in cm) of a circle whose radius is 18 cm. OA circle with a radius of 18 cm. c. If f(a) = 18, what does a represent in this context? Select all that apply. OA circle with a circumference of 18 cm. OThe radius (in cm) of a circle whose circumference is 18 cm. OA circle with a radius of 18 cm. OThe circumference (in cm) of a circle whose radius is 18 cm. d. What values can r assume in this context? Express your answer as an interval. Preview e. What values can f(r) assume in this context? Express your answer as an interval. Preview